In this study, the distributions of insulin binding sites on the surface of rat adipocytes and liver plasma membranes were studied using monomeric ferritin-insulin viewed by electronmicroscopy and analyzed by newly developed quantitative methods. It shows that insulin binding sites are non-randomly distributed on rat adipocyte cell surfaces while they are uniformly distributed on liver plasma membranes. The quantitative characteristics of the receptor groups and the mode of action of cytochalasin B and D have been elucidated. In the second part we have been looking at the organization of intramembraneous particles on lymphocytes and coated pits on adipocyte-like fibroblasts. In the third part of this investigation, the three dimensional structure of polymerization centers for macromolecules in cells has been pursued using three-dimensional reconstruction and image analysis techniques. The fourth part is an experimental study of the effects of aggregation of membrane proteins on the organization and polymerization of cytoskeletal elements inside cells and its relation to transmembrane signalling.